** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** SULFUR (S) IS A MAJOR PLANT NUTRIENT REQUIRED FOR SYNTHESIS OF THE ESSENTIAL AMINO ACID METHIONINE AND NUMEROUS OTHER S COMPOUNDS THAT ARE FUNDAMENTAL FOR PHYSIOLOGICAL PROCESSES LIKE CARBON ASSIMILATION, NUTRIENT UTILIZATION, ABIOTIC STRESS RESPONSES, AND OVERALL PLANT PRODUCTIVITY. IN LEGUMES, SUCH AS PEA AND SOYBEAN, S IS ESPECIALLY CRITICAL FOR FIXATION OF ATMOSPHERIC NITROGEN IN ROOT NODULES, AND FOR THE SYNTHESIS OF HIGH QUALITY, S-RICH SEED STORAGE PROTEINS. BASED ON OUR PRELIMINARY RESULTS, WE HYPOTHESIZE THAT S PARTITIONING PROCESSES FROM SOURCE TO SINK PLAY A CENTRAL ROLE IN NODULE METABOLISM AND SEED S NUTRITION, AND THAT S TRANSPORTERS LOCATED IN SOURCE AND SINK REGULATE THE AMOUNT AND TYPE OF S COMPOUNDS MOVED TO NODULES AND SEEDS, THEREBY CONTROLLING THEIR PHYSIOLOGY. WE FURTHER PREDICT THAT ALTERATIONS IN S TRANSPORT PROCESSES WILL LEAD TO ADJUSTMENTS IN NITROGEN AND CARBON FIXATION RATES, METABOLISM, AND ALLOCATION, AND RESULT IN IMPROVED LEGUME GROWTH AND PRODUCTIVITY. WE HAVE GENERATED UNIQUE PEA AND SOYBEAN LINES OVEREXPRESSING DIVERSE S TRANSPORTERS THAT WILL ENABLE US TO DETERMINE THE ROLE OF S PARTITIONING PROCESSES IN BIOLOGICAL NITROGEN FIXATION IN NODULES (OBJECTIVE 1), AS WELL AS IN SEED YIELD AND SEED NUTRITIONAL QUALITY (OBJECTIVE 2). WE WILL FURTHER RESOLVE THE FUNCTION OF S TRANSPORTERS IN SINK METABOLISM UNDER S DEFICIENCY, AND THEIR CONTRIBUTION TO S USE EFFICIENCY (OBJECTIVE 3). OUR LONG-TERM GOAL IS DISCOVERY TRANSFER LEADING TO ENHANCED CROP PRODUCTIVITY, IMPROVED NUTRITIONAL VALUE OF PLANT PRODUCTS, AND INCREASED RESILIENCE TO NUTRIENT DEFICIENCY AND POTENTIALLY OTHER ENVIRONMENTAL STRESSES.